Semiconductor switching device



Nov. 27, 1962 A. J. w. M. VAN ovERBEEK ETAL 3,066,258

sEMrcoNDucToR swITcHING DEVICE Original Filed Deo. '7, 1954 l# Sii-.6 4 55.7

INVENTQSRS E. WILLE A.J.YI.M. VAN OVERBEEK BY J.T.A. VAN LOTTUM d am AGE

United States Patent Oil-ice 3,056,258 Patented Nov. 27, 1962 3,ti6,258 SEMICNDUC'ER SWIICi-IING DEVICE Adrianus I. W. M. van verheeir, Ehertus Willems, and

Johannes Theodorus Antonius van Lottum, all of Eindhoven, Netheriauds, assignors, by mesne assignments, to North American Philips Company, Inc., New York, NX., a corporation of Delaware Original appiication Dec. 7, 1954, Ser. No. 473,624.1, now Patent No. 2,935,623, dated May 3, 1950. Divided and this application Jan. 20, 196i), Ser. No. 9,663

1 Ciaim. (Cl. 324-110) The present application is a division of U.S. patent application Serial No. 473,624, filed December 7, 1954, now Patent No. 2,935,623.

The present invention relates to semiconductor switching devices. The principal object of the invention is to provide a circuit including an impedance which, under the action of a switching quantity, changes from a comparatively low to a comparatively high value.

A circuit arrangement according to the invention comprises an electric line and a transistor having an emitter electrode, a collector electrode and a base region; means are provided for connecting the emitter-collector path of the transistor in the line and means such as capacitors are also connected in the line for preventing direct current iiow in the line. In the normal condition of the circuit, the emitteneollector path presents a comparatively high impedance in `the line thereby substantially opening the line. Means are also provided for producing a current ow of predetermined magnitude in the base region o the transistor; upon the application of this current tlow, the emitter-collector path presents a comparatively low impedance in the line, thereby substantially closing the line. More particularly, a switching quantity is supplied to the transistor; this may comprise a switching voltage applied to the base of a transistor triode or a switching luminous ux impinging on the base region of a photo-transistor. The invention will now be described more fully with reference to the accompanying drawing, in which:

I' FIG. l is a schematic diagram of an embodiment of the circuit arrangement of the invention utilizing a transistor triode;

FIG. 2 is a schematic diagram of an embodiment of the circuit arrangement of the invention utilizing a phototransistor;

FIG. 3 is a series of current versus voltage characteristie curves for the circuit arrangement of FIGS. l and 2;

FIG. 4 is a schematic diagram of an embodiment of the circuit arrangement of the invention for substantially short-circuiting or interrupting an electric line;

FIG. 5 is a schematic diagram of a modification of the embodiment of the circuit arrangement of FIG. 4;

FIG. 6 is a schematic diagram of another embodiment of the circuit arrangement of the invention;

FIG. 7 is a schematic diagram of a modiication of the embodiment of FIG. 6; FIG. S is a schematic diagram of au embodiment of the circuit arrangement of the invention for limiting electric signals;

FIG. 9 is a schematic diagram of an embodiment of the circuit arrangement of the invention for safeguarding a measuring instrument; and

FIG. l() is a schematic diagram of an embodiment of the circuit arrangement ot the invention for stabilizing the operative or non-operative condition of an oscillator.

FIGS. l and 2 are circuit arrangements in accordance with the invention, which consist of an electric circuit l in which, due to the provision of blocking capacitors 2 and 3, neither direct voltage is operative, nor direct current flows and which includes the emitter-collector path of a junction transistor di or 4', respectively. In FIG. l

the transistor 4 is of the triode type and in its base circuit a current source l6 is connected for generating a base current Ib. In FIG. 2 the transistor 4' is a photo-transistor in which by means of a light source 7 free carriers are produced.

FIG. 3 is a curve family of a junction transistor which is known per se and in which the collector direct current l., is plotted as a function of the collector direct voltage VC at different values of the base current Ib; the currents and voltages concerned are positive if they correspond to the direction of the arrows or to the signs -1- respectively in FIG. l. These curves relate more particularly to transistors of the symmetrical kind which, as is well known, exhibit substantially identical characteristics when the emitter and the collector are interchanged. Entirely analogous characteristic curves are found for the Ic--Vc curves of a symmetrical photo-transistor at different values of the incident luminous ux L, as is indicated in brackets in FIG. 3; the designation is the same as in the case of FIG. 2.

The circuits of FIGS. `l and 2 behave as a variable resistance. Since in accordance with the invention the direct voltage VG between the emitter and the collector is equal to zero, the operating point of the transistors 4 and 4 respectively is coincident with the origin 0 of the co ordinates shown in FIG. 3. At this adjustment they present a comparatively high resistance of, for example, from a few hundred kilohms to a few megohms, if lb=0 or L=0 respectively; this resistance corresponds to the slope of the curve a in FIG. 3. If Ib or L respectively exceeds zero, a comparatively low resistance of, for example, less than ohms is found, which resistance corresponds to the branch b in FIG. 3. Switching-over the current Ib or the luminous uX L, respectively, consequently permits this resistance to vary from a comparatively high value to a comparatively low value and vice versa so that the circuit is substantially interrupted or closed respectively.

On the other hand, a similar considerable resistance variation is found, if Ib or L respectively are adjusted at a predetermined value, in which case the curve c may, for example, apply, and the signal current passing through the circuit 1 momentarily exceeds one of the bending points d of this curve. This resistance variation may in this case be used to limit the signal current.

FIG. 4 is an embodiment for substantially closing and interrupting an electric line. One line Il of a two-wire electric line 11-12 comprises a circuit I which comprises the emitter-collector paths of a transistor I3 of pnp conductivity type and of a transistor 14 of npn conductivity type; between the bases of the transistors 13 and 14 a switching voltage source I5 is connected with a polarity which may be reversed by means of a commutator I6. I-Icre also the blocking capacitors 2 and 3 connected in the line Il prevent any direct current supplied from the source 15 from owing o through said line.

In the position of the commutator of FIG. 4, the source 15 tends to pass a negative base current Ib so that the transistors 13 and 14 are adjusted at an operating line corresponding to the curve a shown in FIG. 3. Since in this case also, due to the provision of the capacitors 2 and 3, the mean collector voltage Vc across each of the transistors 13 and I4 is equal to zero, the adjusting point of these transistors consequently again corersponds to the origin lof the co-ordinates shown in FIG. 3. In this adjusting point the said operating line a presents a high differential resistance so that the line 11 may be regarded as substantially interrupted.

=If the commutator 16 is reversed, the source I5 causes a positive base current Ib to dow, with the result that the transistors I3 and 14 `are adjusted at the operating 3% line b which in the origin presents a very small differential resistance so that the line lll may be regarded as substantially closed.

A further improvement is obtained if, as shown in the embodiment of FIG. 5, the line portion i8 between the two transistors ll3 and i4 is Connected to the line 12 through a resistance 19, which is small compared with the diierential resistance of the branch a but large compared with that of the branch b in FIG. 3. The resistance 19 draws the greater part of the signal currents still passed, due to its comparatively small value, if the line lll is desired to be interruped, whereas, if the line 11 is desired to be closed, it will cause only a slight attenuation of the passed signal currents. If a point of the circuit between the two bases is desired to be connected to the line 12, which may be connected to ground, it will generally be preferable for this connection to be made at a point of symmetry of the circuit arrangement in order to insure a symmetrical operation of the transistors i3 and 14.

PEG. 6 is an alternative circuit arrangement for substantially short-crircuiting or interrupting respectively an electric lead, in which the lead lll includes only the emitter-collector-path of one signal transistor 13 in the base circuit of which the switching voltage source 15 is again operative with a polarity which may be reversed by means of a commutator i6. The circuit for the source 15 is closed through two resistances i21 and 22 connected to the line VVl2. The value of the resistances 21 and 22, similarly to that of the resistance 19 shown in FIG. 5, is again required to be small compared with the differential resistance of the curve a but large compared with that of the curve b in FIG. 3. A resistance 23 of suilicient value prevents the signal currents from being short-circuited.

FIG. 7 is a modification of the circuit arrangement of FIG. 6 comprising a photo-transistor 24 which may or may not be irradiated by the light source 7, and accordingly presents a comparatively small or comparatively large resistance, respectively. reason t-o that described with reference to FIG. 6, resistances 2l and 22 of the value indicated for FIG. 6 may be provided.

In the circuit arrangements of FIGS. 4 to 7 the source 15 or the source 7 is generally required to supply such an amount of current or light respectively that the signal currents passing through the line 11 do not exceed the bending points (for example d) of the curves shown 1n FIG. 3, in order to avoid signal limitation. However, the Vrequired respective current intensity or luminous intensity is very slight, as may be seen from the numerical values given by way of example in FIG. 3.

FIG. 8 is a circuit arrangement for limiting electric signal oscillations. rlhese oscillations are supplied from a signal source 25 through the emitter-collector path of a transistor 4 to an output impedance 27, which is again small compared with the differential resistance of the curve a but large as compared with that of the curve b shown in FIG. 3. A supply source 2S supplies a constant small base current to the transistor 4, with the result that curve c, for example, of FIG. 3 applies to the transistor 4. i

So long as the signal currents passing through the Vtransistor 4 are maintained smaller than corresponds to the bending points d yof this curve, the transistor 4 presents a comparatively slight resistance which is equal to the differential resistance of the branch b in FIG. 3. However, as soon as these points are exceeded, this resistance becomes comparatively large. That is, the said resistance becomes equal to the differential resistance of the branch e in FIG. 3 which is approximately equal to thatof the branch a. Consequently, across the impedance 27 are produced limited signal voltages, the maximum value of which approximately corresponds to Vthe current values of the points d in FIG. 3. If in this lf desired, for a similar case the transistor 4 is of the symmetrical type, a symmetrical limitation of the positive and the negative phases of the signal current is produced. On the other hand, in a transistor 4 of the unsymmetrical kind an unsyrnmetrical limitation is produced.

A similar limiting arrangement can be obtained by substituting a photo-transistor for the transistor 4 and a light source for the supply source 28. In this case the operation is entirely analogous to that of the arrangement of FIG. 8.

FIG. 9 is an arrangement for safeguarding a measuring instrument, more particularly a galvanometer 32 connected in the diagonal arm of a measuring bridge 31. If one of the impedances of the bridge 31 is required to be measured by varying one or more further known impedances of the bridge until the galvanometer 32 indicates zero, at the beginning of the measurement the bridge will generally be unbalanced so that a considerable current flows through the diagonal arm. This current is maintained within predetermined limits by connecting a phototransistor 24, which is irradiated by an incandescent lamp 7, in series with the galvanometer 32; the eiective resistance of said transistor in the substantially non-conductive condition is large compared with that of the galvanometer.

FlG. l0 is an oscillator arrangement the on and oil conditions of which are stabilized. The oscillator consists of a transistor 36 provided with regenerative feedback by means of a transformer 3S. The transistor 36 is prevented from spontaneous oscillation (oi condition) by the provision of a damping resistance connected in parallel with the feed-back circuit. The said resistance consists of the emitter-collector path of a transistor 4, which is adjusted at a bias voltage corresponding to the pass direction of the emitter-collector path and consequently presents only a low resistance which is equal to the diierential resistance of the branch b shown in FIG. 3.

i The base of the transistor 4 is connected to its emitter through a capacitor 37. If a pulse 38 is supplied to one of the circuits of the circuit arrangement, e.g. in series with the capacitor 37, or if the capacitor 37 is short circuited for a short period of time so that the transistor I4 is operated at its curve a, the damping in the feed-back circuit of the transistor oscillator 3536` is so slight that the oscillator is enabled to oscillate spontaneously (-on condition). The produced oscillator oscillations are detected in the collector-base blocking layer of the transistor 4. Thus the base of the transistor 4 has a potential applied to it which corresponds to the blocking direction of the emitter-base path, so that said transistor continues to operate at its curve a, and consequently continues to cause a'substantially negligible damping of the oscillator 35--36.

In the circuit-arrangement of FIG. 10a similar eiect may also be obtained by substituting an RC filter for the capacitor 37 in the Vemitter circuit of the transistor'i4. However, it is found that in this case satisfactory operation requires the use of a larger oscillator amplitude and the transistor 4 in the on condition of the oscillator 35-36 produces a heavier damping. The left hand terminal of the capacitor 37 may obviously also be connected to the negative terminal of the supply source so that it is connected to the emitter of the transistor 4 via the supply source.

What is claimed is:

A circuit arrangement comprising an electric measuring instrument, a transistor having an emitter electrode, a collector electrode and a base electrode, means for connecting the emitter-collector path of said transistor directly in series with said instrument, means for applying signals to be measured to the series .connection of said instrument and the emitter-collector path of said transistor, and means for initiating a current flow of predetermined magnitude in said base electrode whereby when said signals are smaller in magnitude than a predetermined Value the emitter-collector path of said transistor presents a comparatively low impedance thereto and when said input signals are larger in magnitude than said predetermined 5 6 value said emitter-collector path presents a comparatively 2,763,832 Shockley Sept. 18, 1956 high impedance thereto -thereby protecting said instru- 2,890,352 Goodrich June 9, 1959 ment from overload. 2,921,264 Sundt Ian. 12, 1960 OTHER REFERENCES References Cited in the tile of this patent 5 P by I s 1 P f T t d tt u 1cat1on: ymmetrlca roperties o ransls ors` an UNITED STATES PATENTS Their Applications, by G. F. Sziklai in Proceedings of the 2,759,052 Macdonald Aug. 14, 1956 I.R.E., pages 717-724, June 1953. 

